Off-road excavation machines are commonly used to efficiently provide a number of different excavation related functions. An example type of excavation machine is a trencher. Trenchers are typically used to excavate trenches for use in installing utilities such as underground pipe or conduit for cable. A trencher generally includes a chassis supported on a propulsion system having ground engaging tracks or tires. A trenching boom is pivotally connected to the chassis and is pivotally movable relative to the chassis between a raised transport position and a lowered trenching position. For excavating trenches in rocky or hard packed ground, a rotatable rock wheel may, in one embodiment, be mounted to the trenching boom. The rock wheel includes a plurality of excavating teeth positioned around the wheel's outer periphery.
To power the rotation of the rock wheel, a motor, or a pair of motors, is attached directly to the rock wheel. Each motor is then attached to the boom. However, when fixing the motors to the boom, the input shafts of each motor and the rotational shaft of the rock wheel are difficult to align. When the input shafts are misaligned with the rock wheel rotational shaft, indeterminate static loading can result in loading conditions where the various components of the system are subjected to excessive loads. More generally, such an issue arises when attempting to mount a rotating shaft to fixed structures while also attempting to align the shaft to prevent excessing loading within the associated system. Schematic examples are shown in FIGS. 1A and 1B.
As shown, input shafts 10 are mounted to a rotating structure 12. Each input shaft 10 is supported in a motor housing 14 which are each secured to a fixed frame structure 16 at sides A and B, respectively. As shown in FIG. 1A, the input shaft 10 mounted at side A is supported in the motor housing 14 by a pair of bearings 18, while the input shaft 10 mounted at side B is supported in the motor housing 14 by a single bearing 18. Because side B is skewed with respect to the side A, the single bearing 18 at side B must either 1) move so as to align its centerline with an axis of rotation X of the input shaft 10; or 2) the motor housing 14 must move so as to align the axis of rotation X of the input shaft 10 with the centerline of the bearing 18. Conversely, FIG. 1B shows two bearings 18 supporting the input shaft 10 at side B. When compared to the example shown in FIG. 1A, the bearings 18 in FIG. 1B cannot be repositioned along the input shaft 10 so as to perfectly align the axis of rotation X of the input shaft 10 within the centerlines of the bearings 18. Therefore, this example is said to be statically indeterminate as it provides a situation where the resulting loads on the components of the mounting system are not possible to calculate without defining certain properties of components in the system, such as the stiffness of the frame 16 and the motor housing 14.
Because both of the examples shown in FIGS. 1A and 1B show a motor housing 14 fixedly secured to the frame structure 16, movement of the motor housings 14 is not possible, nor feasible. Because of this, indeterminate static loading is created which results in loading conditions where the various components of the system are subjected to excessive loads. These loads that can fluctuate as a function of the rotational position of the rotating structure 12. Additionally, the loads are created by the amount of misalignment of the sides A and B of the frame 16 and also can be a function of the rigidity of the frame 16 and the amount of misalignment of the sides A and B of the frame 16. The components of the system that are affected include the bearings 18, the motor housing 14, and the frame 16 and such loading can lead to failure of such components.
Therefore, improvements in mounting such motors are needed.